Metformin, a medication commonly taken for Type II diabetes, is being found in freshwater systems worldwide, and a new study says that it causes physical changes in male fish exposed to doses similar to the amount in wastewater effluent. It causes intersex in fish - male fish that produce eggs - according to the study in Chemosphere.
Because intersex fish occur more often downstream from wastewater treatment plants, studies have investigated the effect of hormones from birth control pills, but metformin is not a hormone and it targets blood sugar regulation so the correlation is surprising.
Professor Rebecca Klaper in the School of Freshwater Sciences at the University of Wisconsin-Milwaukee, says it is also prescribed to women with a common hormonal disease called polycystic ovary syndrome. The research in her lab indicates metformin could be a potential endocrine disruptor - a chemical that confuses the body's complicated hormonal messaging system, interrupting a range of normal activities, including reproduction.
Of the chemicals she has detected in water samples collected from Lake Michigan, metformin stands out, Klaper said. "It is the chemical we found in almost every sample and in the highest concentrations compared to other emerging contaminants - even higher than caffeine."
In a previous study, Klaper exposed mature fish to metformin, and although there were no physical changes, they found the genes related to hormones for egg production were being expressed in males as well as females - an indication of endocrine disruption.
For the current study, the researchers monitored fish that had continuous exposure to metformin from birth to adulthood. The next step is to determine the corresponding changes in the genome.